Booster Injection with Birch Pollen Extract Activates B‐Cellular Memory Responses in Patients Having Completed Allergen Immunotherapy

Allergen immunotherapy (AIT) of patients with IgE‐mediated allergy results in the synthesis of blocking IgG antibodies mediating allergen tolerance. However, as antibody concentrations wane after stopping AIT, tolerance may be lost. The impact of a single booster allergen application on B‐cellular memory in AIT‐treated birch pollen (BP)‐allergic patients was investigated. Twenty‐five patients with BP allergy who finished AIT 3–12 years ago received one allergen injection approximately 4 months prior to the next BP season. We determined peripheral Bet v 1‐specific IgG‐secreting cells (ASC) by ELISPOT analysis and BP‐specific IgG, IgG4, and IgE serum antibodies by ImmunoCAP, and the allergen‐blocking capacity of IgG/IgG4 antibodies by ELIFAB assay. Clinical responses were assessed by visual analog scales. Immunological findings were compared with the primary B cell response of 12 BP‐allergic patients receiving conventional AIT. Bet v 1‐specific ASC significantly increased 2–4 weeks after BP‐injection, accompanied by enhanced levels of both BP‐specific IgG/IgG4 antibodies and allergen‐blocking serum activity. Compared with conventional up‐dosing, a single booster vaccination led to a markedly stronger B cell response after 4 weeks. Allergen booster injection activates B‐cellular memory associated with blocking IgG/IgG4 antibodies, pointing to reinforcement of allergen tolerance after completion of AIT.